DETECTION SYSTEM FOR OCULAR REFRACTIVE ERROR MEASUREMENT

An automatic and objective system for measuring ocular refractive erro rs (myopia, hyperopia and astigmatism) was developed. The system consi sts of projecting a light target (a ring), using a diode laser (lambda = 850 nm), at the fundus of the patient's eye. The light beams scatte red from the retina are submitted to an optical system and are analyse d with regard to their vergence by a CCD detector (matrix). This syste m uses the same basic principle for the projection of beams into the t ested eye as some commercial refractors, but it is innovative regardin g the ring-shaped measuring target for the projection system and the d etection system where a matrix detector provides a wider range of meas urement and a less complex system for the optical alignment. Also a de dicated electronic circuit was not necessary for treating the electron ic signals from the detector las the usual refractors do); instead a c ommercial frame grabber was used and software based on the heuristic s earch technique was developed. All the guiding equations that describe the system as well as the image processing procedure are presented in detail. Measurements in model eyes and in human eyes are in good agre ement with retinoscopic measurements and they are also as precise as t hese kinds of measurements require (0.125D and 5 degrees).